Polymerization method

ABSTRACT

The present disclosure is directed to a catalyst comprising the reaction product of: 
     (a) a silicon-containing compound having the structural formula R 4--n  SiX n  --where R is C 1  -C 10  hydrocarbyl; X is halogen; and n is an integer of 1 to 4; 
     (b) a magnesiumdialkyl having the structural formula R 1  R 2  Mg, where R 1  and R 2  are the same or different and are C 2  -C 10  alkyl; 
     (c) an alcohol having the structural formula R 3  OH, where R 3  is C 1  -C 10  hydrocarbyl; 
     (d) a halide-containing metal compound, said metal selected from the group consisting of titanium, zirconium and vanadium; 
     (e) an aluminum alkoxide having the structural formual Al(OR 5 ) 3 , where R 5  is C 2  -C 4  alkyl; and 
     (f) a halide-containing metal compound said metal selected from the group consisting of titanium, zirconium and vanadium, with the proviso that said reaction product is formed from said components (a) to (f) reacted in the order recited but for the interchangeability of components (a) and (b). 
     The catalyst of this disclosure is useful, when provided in a catalytically effective amount and in the presence of co-catalytically effective amount of an organoaluminum compound, in the polymerization of alpha-olefins.

This is a divisional of copending application Ser. No. 427,071, filed onOct. 25, 1989 now U.S. Pat. No. 5,01,099.

BACKGROUND OF THE DISCLOSURE

1. Field of the Invention

The present invention is directed to a polymerization catalyst. Moreparticularly, the present invention is directed to a catalyst useful inthe polymerization of at least one alpha-olefin.

2. Background of the Prior Art

There is a probably no subdivision of catalysis that has been asthoroughly developed as the catalytic polymerization of olefin polymers.Catalysts employed in the polymerization of olefins, especiallyalpha-olefins, more particularly, ethylene, have been the subject ofinnumerable patents and technical articles. In recent years, aparticularly active sector of this technology has focused upon thecatalytic formation of so-called "linear low density polyethylene"(LLDPE).

LLDPE, although employed in similar applications as earlier developedlow density polyethylene (LDPE), represents an advance in the art inthat the polymerization of LLDPE is far less difficult than is thepolymerization of LDPE. That is, whereas LDPE is polymerized under veryhigh pressure, with all the complications attendant therewith, morerecently developed LLDPE is polymerized at far lower pressure,simplifying and easing the costs and complications of this reaction.Because LDPE and LLDPE, although chemically distinct, can be utilized inthe same applications, this new polymer has rapidly grown in commercialimportance.

The development of LLDPE has spurred a parallel development of catalystsuseful in its polymerization. Two major goals have been focused upon inevaluating a catalyst useful in the polymerization of LLDPE. The firstof these factors is the effect of the catalyst on higher alpha-olefincomonomer incorporation in the LLDPE. As those skilled in the art areaware, LLDPE is a copolymer of ethylene and a higher alpha-olefin,usually a C₄ to C₁₀ alpha-olefin. A common problem associated with thecatalysts of the prior art employed to polymerize LLDPE has been thepoor incorporation of the higher alpha-olefin in the final copolymer.

A LLDPE typically incorporates up to about 10 weight percent of a higheralpha-olefin, based on the total weight of the ethylene-higheralpha-olefin copolymer. Although only up to about 10 weight percent ofthe higher alpha-olefin is included in the copolymer, unfortunately, amuch higher concentration of the higher alpha-olefin must be reacted toproduce this result. This, of course, results in higher processingexpense in that the higher alpha-olefin must be heated and pressurizedalthough it is not polymerized. Thus, an aim of LLDPE catalyst designerscontinues to be the development of a catalyst which more efficientlyincorporates the higher alpha-olefin monomer charged in thepolymerization reactor into the copolymer product.

The second major goal by which a catalyst is judged in thepolymerization of LLDPE is its hydrogen response That is, hydrogen ischarged into ethylene polymerization reactors to modify the polymer'sdegree of polymerization. This degree of polymerization is manifested,in the case of an ethylene polymer, by its melt index. If the degree ofpolymerization is too high, its viscosity is excessive, as defined by avery low melt index. Thus, hydrogen is incorporated in thepolymerization reaction to ensure that the degree of polymerization isnot excessive. That is, hydrogen is added to guarantee that the LLDPEmelt index is sufficiently high. As in the case of higher alpha-olefinincorporation, increasing inclusion of hydrogen increases the cost ofpolymerization. That is, greater concentrations of unreacted hydrogenresult in greater thermodynamic costs of heating and pressurization.Thus, the lesser amounts of hydrogen necessary to produce reasonablemelt index LLDPE products result in more attractive polymerization. Thisresult is a function of the polymerization catalyst. Thus, a criticalproperty of a LLDPE catalyst is its so-called "hydrogen response," theability of the catalyst to efficiently utilize the hydrogen present tomodify the degree of polymerization of the LLDPE product.

The development of LLDPE polymerization catalysts has not, in the priorart, reached a point where these desirable properties have beenoptimized. There are, however, a multiplicity of known catalysts whichwill be recognized as being similar, in their method of formation, tothe catalyst of the present invention.

For example, U.S. Pat. No. 4,252,670 describes an olefin polymerizationcatalyst formed by treating a magnesium hydrocarbyl, or a complex ormixture of a magnesium hydrocarbyl compound and an aluminum hydrocarbylcompound, with at least one halogenating agent; reacting this productwith a Lewis Base, which may be an ether, an ester, a ketone, analcohol, a thioether, a thioester, a thioketone, a thiol, a sulfone, asulfonamide or the like; and then reacting the thus formed reactionproduct with titanium tetrachloride

U.S. Pat. No. 4,496,660 describes a catalyst for the polymerization ofolefins which is initially the reaction product of a hydrocarbylmagnesium compound or a bonded mixture of a hydrocarbyl magnesium and ahydrocarbyl aluminum, zinc or boron, and an oxygen-containing and/ornitrogen-containing compound, such as an alcohol or an amine. Thisinitial reaction product is reacted with a halide source, ahalide-containing aluminum, silicon, tin, phosphorus, sulfur, germanium,carboxy, hydrogen, hydrocarbyl or Group IV-B metal, Group V-B metal,Group VI-B metal compound or mixtures thereof. This product, in turn, isreacted with a transition metal compound, which may be titaniumtetrachloride, and with a reducing agent, a boron, aluminum, zinc ormagnesium organic compound, to form the catalyst.

U.S. Pat. No. 4,295,992 describes an olefin polymerization catalystformed by the reaction of an aliphatic alcohol with a mixture of andialkylmagnesium compound and a silicon tetrahalide. This product isthen treated with an organic titanium compound, such as titaniumtetrachloride, and, finally, with a suitable reducing agent, such asdiethylaluminum chloride.

Although the above discussed prior art disclosures advance the artinvolving the catalytic polymerization of alpha-olefins, none of them,nor any other of innumerable other prior art references, areparticularly useful in the polymerization of LLDPE. That is, nopolymerization catalyst has been identified which both polymerizesethylene and is characterized by excellent hydrogen response as well ashigher alpha-olefin copolymer incorporation capability.

SUMMARY OF THE INVENTION

A new catalyst has now been developed which is particularly suited forpolymerization of linear low density polyethylene in that it providesboth excellent capability of higher alpha-olefin incorporation andexcellent hydrogen response. Its use in the polymerization of ethyleneand a higher alpha-olefin results in the formation of LLDPE with minimumexcess higher alpha-olefin comonomer and minimum hydrogen usageconsistent with the polymerization of the desired LLDPE.

In accordance with the present invention, a catalyst is provided. Thecatalyst comprises the reaction product of:

(a) a silicon-containing compound having the structural formula R_(4--n)SiX_(n), where R is C₁ -C₁₀ hydrocarbyl; X is halogen; and n is aninteger of 1 to 4;

(b) a magnesiumdialkyl having the structural formula R¹ R² Mg, where R¹and R² are the same or different and are C₂ -C₁₀ alkyl;

(c) an alcohol having the structural formula R³ OH, where R³ is C₁ -C₁₀hydrocarbyl;

(d) a halide-containing metal compound, said metal selected from thegroup consisting of titanium, zirconium and vanadium;

(e) an aluminum alkoxide having the structural formula Al(OR⁵) where R⁵is C₂ -C₄ alkyl; and

(f) a halide-containing metal compound, said metal selected from thegroup consisting of titanium, zirconium and vanadium, with the provisothat said reaction product is formed from said components (a) to (f)reacted in the order recited except for the interchangeability ofcomponents (a) and (b).

In further accordance with the present invention, a process forpolymerizing alpha-olefins is provided. In this process at least onealpha-olefin is polymerized, under alpha-olefin polymerizationconditions, in the presence of a catalytically effective amount of thecatalyst of the present invention and in the further presence of aco-catalytically effective amount of a trialkylaluminum compound.

DETAILED DESCRIPTION

The catalyst component of the present invention comprises the reactionproduct of a series of six independent compounds. The first twocompounds are a silicon-containing compound and a magnesiumdihydrocarbyl. The order of addition of these two compounds isindependent. That is, either component may be added to the other toproduce a first reaction product.

The silicon-containing compound, the first component, has the structuralformula

    R.sub.n-4 SiX.sub.n                                        (I)

where R is C₁ -C₁₀ hydrocarbyl; X is halogen; and n is an integer of 1to 4. Preferably, the silicon-containing compound has the structuralformula I where R is C₁ -C₁₀ alkyl; X is chlorine or bromine and n is aninteger of 2 to 4. More preferably, the silicon-containing compound ischaracterized by structural formula I where R is C₁ -C₄ alkyl; X ischlorine or bromine; and n is an integer of 3 or 4. Still morepreferably, the silicon-containing compound is defined by structuralformula I where X is chlorine or bromine and n is 4. Most preferably,the silicon-containing compound is silicon tetrachloride.

Among the silicon-containing compounds within the contemplation of thepresent invention are dimethylsilicon dichloride, methylsilicontrichloride, diethylsilicon dichloride, triethylsilicon chloride,ethylsilicon trichloride, di-n-butylsilicon dibromide di-n-propylsilicondichloride, n-butylsilicon tribromide, di-n-butylsilicon dichloride,trimethylsilicon chloride, triethylsilicon bromide, silicontetrabromide, silicon tetrachloride and the like. It is emphasized thatthis group is non-inclusive and other compounds within generic formulaof the silicon-containing compound of this invention are within thecontemplation of this invention. Of the silicon-containing compoundswithin the contemplation of this invention silicon tetrabromide andsilicon tetrachloride are particularly preferred, with silicontetrachloride most preferred.

The second component, reacted with the silicon-containing compound,included in the catalyst of the instant invention, is a magnesiumdialkylhaving the structural formula

    R.sup.1 R.sup.2 Mg                                         (II)

where R¹ and R² are the same or different and are C₂ -C₁₀ alkyl.Preferably, the magnesiumdialkyl has the structural formula I where R¹and R² are the same or different and are C₂ -C₆ alkyl. More preferably,the magnesiumdialkyl is characterized by the structural formula II whereR¹ and R² are the same or different and are C₂ -C₄ alkyl.

Included among the magnesiumdialkyl compounds within the contemplationof this invention are diethylmagnesium, di-n-propylmagnesium,diisopropylmagnesium, di-n-butylmagnesium, n-butyl-sec-butylmagnesium,ethylbutylmagnesium, n-propyl-n-butyl-magnesium and the like. Again,this grouping is given for illustrative purposes only and the many othercompounds within the generic meaning of structural formula II, notmentioned above, are within the contemplation of this invention. Ofparticular applicability in the catalyst of this invention is the use ofdi-n-butylmagnesium and n-butyl-sec-butylmagnesium.

As stated above, the silicon-containing compound and themagnesiumdialkyl compound are reacted with each other in either order.That is, the silicon-containing compound may be added to themagnesiumdialkyl or vice versa. It is preferred, however, to add themagnesiumdialkyl to the silicon-containing compound.

This reaction is preferably conducted in solution. A common solvent forthe silicon-containing compound and the magnesiumdialkyl is usuallyemployed. A preferred solvent for use in this application is a C₅ -C₁₀alkane. Among the preferred alkanes useful as the solvent in thereaction of the silicon-containing compound and the magnesium dialkylcompound are hexane and heptane. Heptane is particularly applicable forthis application.

The reaction product of the silicon-containing compound and themagnesiumdialkyl is, in turn, reacted with an alcohol. The alcohol,useful in the formation of the catalyst of this invention, ischaracterized by structural formula

    R.sup.3 OH                                                 (III)

where R³ is C₁ -C₁₀ hydrocarbyl. Preferably, the alcohol of the presentinvention is defined by structural formula III where R³ is C₁ -C₁₀alkyl. Thus, it is preferred that the alcohol be an alkanol. Morepreferably, the alcohol having the structural formula III is defined byR³ being C₁ -C₆ alkyl. Still more preferably, the alcohol having thestructural formula III has a R³ meaning of C₁ -C₄ alkyl. Yet still morepreferably, the alcohol has the structural formula III where R³ is C₁-C₂ alkyl. Most preferably, the alcohol component used in the formationof the catalyst of this invention is ethanol.

Among the preferred alcohols useful in this application are methanol,ethanol, n-propanol, isopropanol, n-butanol and the like. Of these,methanol, ethanol, isopropanol and n-propanol are particularlypreferred. Ethanol, as stated in the above paragraph, is particularlypreferred in this application.

As in the formation of the reaction product of the silicon-containingand magnesiumdialkyl compounds, the third reactant, the alcohol, reactedwith the reaction product of the silicon-containing and magnesiumdialkylcompounds, is introduced into the reaction in solution. Again, thepreferred solvent for the alcohol is a C₅ -C₁₀ alkane, the preferredmembers of which are, again, hexane and heptane.

The reaction product of the first three above-enumerated components isreacted with a fourth component, a halide-containing metal compound, themetal of which is selected from the group consisting of titanium,zirconium and vanadium. Preferably, the halide-containing metal compoundwithin the contemplation of the fourth component of the catalyst of thepresent invention, in the event that the metal is titanium or zirconium,is defined by the structural formula

    M(OR.sup.4).sub.p-4 X.sup.1.sub.p                          (IV)

where M is titanium or zirconium; R⁴ is C₁ -C₆ alkyl; X¹ is halogen; andp is an integer of 1 to 4. More preferably, the compound characterizedby structural formula IV is defined by M being titanium or zirconium; R⁴is C₁ -C₄ alkyl; X¹ is bromine or chlorine; and p is an integer of 2 to4. Still more preferably, the compound characterized by the structuralformula IV where p is an integer of 3 to 4. Most preferably, thetitanium or zirconium compound having the structural formula IV ischaracterized by p being 4.

Alternatively, in the preferred embodiment wherein the halide-containingmetal is vanadium, the compound is characterized by a structural formulaselected from the group consisting of

    VX.sup.1.sub.4                                             (V) or

    VOX.sup.1.sub.3                                            (VI)

where X¹ has the meanings given for the compound having the structuralformula IV.

Preferred embodiments of the halide-containing metal compound of thecatalyst of this invention include titanium tetrachloride, titaniumtetrabromide, vanadium tetrachloride, vanadium tetrabromide, vanadiumoxytrichloride, vanadium oxytribromide, zirconium tetrachloride,zirconium tetrabromide, ethoxytitanium trichloride, methoxytitaniumtribromide, dipropoxyzirconium dichloride, dibutoxyzirconium dichlorideand the like. Among the above preferred halide-containing metalcompounds, titanium tetrachloride, titanium tetrabromide, vanadiumtetrachloride, vanadium tetrabromide, vanadium oxytrichloride, vanadiumoxytribromide, zirconium tetrachloride and zirconium tetrabromide aremore preferred. Still more preferably, the halide-containing compound istitanium tetrachloride or titanium tetrabromide, with titaniumtetrachloride being most preferred.

As in the process of the first three components, the reaction step ofincorporating the fourth component of the catalyst of the presentinvention, the halide-containing metal compound, is preferably conductedby dissolving the halide-containing metal compound in a solvent. As inthe earlier reaction steps, the solvent for the fourth component isagain preferably a C₅ -C₁₀ alkane, with hexane or heptane beingparticularly preferred.

The reaction product of the first three components with thehalide-containing metal compound is reacted, in turn, with a fifthcomponent, an aluminum compound having the structural formula

    Al(OR.sup.5).sub.3                                         (VII)

where R⁵ is C₂ -C₄ alkyl. Preferably, the aluminum compound having thestructural formula VII is characterized by R⁵ being C₃ -C₄ alkyl. Morepreferably, the aluminum compound is defined by structural formula VIIwhere R⁵ is C₄ alkyl. Most preferably, the aluminum compound having thestructural formula VII is defined by R⁵ being sec-butyl.

Compounds within the contemplation of the aluminum component of thecatalyst of this invention include aluminum triethoxide, aluminumtri-n-propoxide, aluminum tri-n-butoxide, aluminum tri-sec-butoxide,aluminum tri-tert-butoxide and the like. Of these, aluminumtri-sec-butoxide is particularly preferred.

The aluminum-containing compound is combined into the catalyst of thepresent invention in accordance with the procedures utilized in theincorporation of the earlier described components. That is, the reactionproduct of the first four components is reacted with thealuminum-containing compound. As is the case in the earlier components,the aluminum-containing component is preferably reacted with thereaction product in solution. Therefore, the aluminum-containingcompound is dissolved in a solvent, which is, again, in a preferredembodiment, a C₅ -C₁₀ alkane. As in the earlier compounds the preferredC₅ -C₁₀ alkane solvents are hexane and heptane.

The sixth and final component which, when reacted with the reactionproduct of the first five components, completes the formation of thecatalyst of the present invention, is a halide-containing metalcompound. Although the halide-containing metal compound constituting thesixth component of the catalyst of this invention need not be identicalwith the fourth component, another halide-containing metal compound, itencompasses the same compounds as defined for the fourth component ofthe catalyst of this invention. The preferences recited in thediscussion of the fourth component apply equally to the degree ofpreference of compounds within the generic meaning of the sixthcomponent. Of course, the halide-containing metal compound constitutingthe sixth component of the catalyst, may be the same compound as thecompound constituting the earlier discussed fourth componenthalide-containing metal compound. Suffice it to say, the preferred,still more preferred and most preferred embodiments of thehalide-containing metal compound sixth component, as well as theexemplifications thereof, are identical with that of thehalide-containing metal compound fourth component of this catalyst. Whenthe most preferred embodiment of both the fourth and the sixthcomponents are used, the compound is titanium tetrachloride and thecompound utilized for the fourth and sixth reacting component of thecatalyst is obviously the same.

The incorporation of the sixth component into the catalyst of thisinvention is, like the first five components, preferably conducted insolution. That is, the halide-containing metal compound is dissolved ina solvent which, as in the earlier components, is preferably a C₅ -C₁₀alkane of which hexane and heptane are the preferred embodiments.

It is emphasized that the sequence of addition of the six componentsthat are reacted together to form the catalyst of this invention is asrecited hereinabove. The only exception to this requirement is theinterchangeability of the first two components. That is, the firstrecited component, the silicon-containing compound, may be added to themagnesiumdialkyl, rather than adding the magnesiumdialkyl to thesilicon-containing compound.

The formation of the catalyst preferably is conducted utilizing specificconcentrations of the above discussed components. For convenience, theseconcentration ranges are predicated on the basis of the molarconcentration of the magnesiumdialkyl, the compound having thestructural formula II. Thus, in a preferred embodiment, the molar ratioof the compound having the structural formula II to thesilicon-containing compound having the structural formula I is in therange of between about 0.1:1 and about 10:1. More preferably, this ratiois in the range of between about 0.2:1 and about 1:1. Most preferably,the molar ratio of compound II to compound I is in the range of betweenabout 0.4:1 and 0.6:1.

The molar ratio of the magnesiumdialkyl reacted in the formation of thecatalyst to the amount of alcohol, the compound having the structuralformula III, reacted in the formation of the catalyst, is preferably inthe range of between about 0.1:1 and about 10:1. This molar ratio ismore preferably in the range of between about 0.2:1 and about 1:1. Mostpreferably, the molar ratio of these reactants is in the range ofbetween about 0.4:1 and about 0.6:1.

The amount of compound having the structural formula IV or, in the casewhere the metal is vanadium, structural formula V or VI, reacted, asexpressed as the molar ratio of the amount of compound II to compoundIV, V or VI is preferably in the range of between about 0.1:1 and about10:1. More preferably, this molar ratio of the magnesium-containingcompound to the compound having the structural formula IV, V or VI is inthe range of between about 0.25:1 and about 5:1. Most preferably, thismolar ratio is in the range of between about 0.5:1 and about 2:1.

The concentration of the fifth component, the aluminum-containingcompound having the structural formula VII, reacted in the formation ofthe catalyst, as manifested by the molar ratio of the concentration ofthe magnesiumdialkyl compound having the structural formula II reactedto that of the compound having the structural formula VII is preferablyin the range of between about 0.05:1 and about 20:1. The molar ratio ofcompound II to compound VII is more preferably in the range of betweenabout 0.1:1 and about 10:1. Most preferably, this ratio is in the rangeof between about 0.5:1 and about 5:1.

The last component utilized in the synthesis of the catalyst, the sixthcomponent having the same structural formulae as compounds IV, V and VI,is present in the catalyst in a concentration such that the molar ratioof compound II to the sixth component is preferably in the range ofbetween about 0.05:1 and about 10:1, more preferably, between about0.1:1 and about 5:1 and most preferably, between about 0.1:1 and about5:1 and most preferably, between about 0.25:1 and about 1:1.

In a preferred embodiment the catalyst may be formulated with theinclusion of an additional reaction step. In this preferred embodimentthe above recited processing scheme for manufacturing the subjectcatalyst is retained. However, the processing steps include theadditional step of initially reacting the silicon-containing compoundhaving the structural formula I, the first component, with an aluminumcompound.

The aluminum compound reacted with the silicon-containing compound hasthe structural formula VII. Indeed, the description given supraregarding the fifth compound defines the aluminum-containing compoundswithin the contemplation of this preferred embodiment. Thus, thepreferred, more preferred and most preferred embodiments of the compoundhaving the structural formula VII of the fifth compound are identical tothe preferred, more preferred and most preferred embodiments of thealuminum-containing compound reacted with the silicon-containingcompound. It follows, therefore, that it is particularly preferred thatthe aluminum-containing compound reacted with the silicon-containingcompound, in this preferred embodiment be the same as the compound whichis utilized as the fifth component in the formulation of the subjectcatalyst. Thus, it is particularly preferred that this compound bealuminum tri-sec-butoxide.

In another preferred embodiment the catalyst includes an inert inorganicsupport. That is, in an another preferred embodiment of the catalyst ofthis invention, the catalyst is prepared in accordance with theprocedure set forth above with the additional inclusion of an inertinorganic additive, which acts as the support, is introduced prior tothe introduction of the above recited components which are combined toproduce the catalyst of this invention.

Preferably, the inert inorganic additive which acts as the support is aninorganic oxide. Among the inorganic oxides within the contemplation ofthe present invention are silica, alumina, zirconia, beryllia and thelike. Of particular application as the inert inorganic support is silicaand alumina. Silica is particularly preferred in this application.

The catalyst of the present invention is utilized in the polymerizationof alpha-olefins. As is common in the catalytic formation ofalpha-olefin polymers, a co-catalyst is utilized with the catalyst ofthis invention wherein, of course, both catalyst and co-catalyst arepresent in catalytically and co-catalytically effective amounts, undersuitable alpha-olefin polymerization conditions, to produce thepolymeric product.

The co-catalyst of the present invention is an organoaluminum compoundPreferably, the organoaluminum compound is a trialkylaluminum compoundcharacterized by the structural formula

    AlR.sup.6.sub.3                                            (VIII)

where R⁶ is C₂ -C₆ alkyl. More preferably, the aluminum compound havingthe structural formula VIII is defined by R⁶ being C₂ -C₄ alkyl.

Preferred co-catalysts within the contemplation of the present inventioninclude triethylaluminum, tri-n-propylaluminum, triisopropylaluminum,tri-n-butylaluminum, tri-sec-butylaluminum, tri-tert-butylaluminum andthe like. Of these, triethylaluminum is particularly preferred.

The polymerization of at least one alpha-olefin occurs under olefinpolymerization conditions. These conditions, in general, embody atemperature of reaction in the range of from about 100° F. to about 220°F., preferably about 140° F. to about 200° F. and most preferably, about160° F. to about 180° F. The pressure of the olefin polymerizationreaction is in the range of from about 50 psi to about 1,000 psi.Preferably, the pressure of reaction is in the range of from about 100psi to about 600 psi. Most preferably, the pressure of the reaction isin the range of from about 300 psi to about 400 psi.

A particularly preferred embodiment of the process of the presentinvention involves the copolymerization of ethylene and a higheralpha-olefin, preferably a C₄ -C₁₀ alpha-olefin, the polymerizationproduct of which is commonly identified as linear low densitypolyethylene (LLDPE). The higher alpha-olefin comonomer employed in thepolymerization, which is usually present in the LLDPE in a weightconcentration of up to about 10% by weight, although introduced into thepolymerization reactor in higher concentration than that, is, in apreferred embodiment, 1-butene. In this polymerization reaction,ethylene and a higher alpha-olefin are introduced into the reactor inthe presence of the catalyst and co-catalyst under the thermodynamicconditions recited above.

The polymerization reactor, in addition to ethylene and the higheralpha-olefin, is also charged with hydrogen. Hydrogen gas has the effectof modifying the degree of polymerization of the LLDPE produced therein.This is manifested by an increase in melt index compared to the meltindex which would characterize the polymerization product in the absenceof hydrogen. Thus, in the preferred embodiment wherein LLDPE ispolymerized two comonomers, ethylene and 1-butene, are charged into areactor that is continuously fed hydrogen.

The following examples are given to illustrate the scope of the presentinvention. Because these examples are given for illustrative purposesonly, it is understood that the scope of the present invention is notlimited thereto.

EXAMPLE 1

Preparation of Catalyst

Silicon tetrachloride (16 ml, 0.14 mole) in heptane (75 ml) was added toa 500 ml, four-necked flask provided with a 60 ml addition funnel,condenser, thermometer and mechanical stirrer. The silicon tetrachloridein solution was heated in the flask to reflux temperature. A 0.68Msolution of dibutylmagnesium in heptane (0.07 mole, 103 ml) was addeddropwise to the flask. The combined contents of the flask were refluxedfor one hour, resulting in the formation of a white solid. Ethanol (0.14mole, 8.2 ml), dissolved in heptane (15 ml), was added dropwise to theslurry and the contents were refluxed for one-half hour. At that point,titanium tetrachloride (0.07 mole, 7.7 ml), dissolved in heptane (10ml), was added and refluxing was continued for an additional two hours.The slurry was cooled to room temperature, the liquid decanted and thewhite solid washed three times, each time with hexane (100 ml).

The thus washed white solid was suspended in hexane (150 ml). Aluminumtri-sec-butoxide (0.07 mole, 17.8 ml), dissolved in hexane (25 ml), wasadded to the slurry. The flask containing this slurry was heated toreflux temperature for one-half hour followed by the addition oftitanium tetrachloride (0.28 mole, 30.8 ml), dissolved in hexane (15ml). This product, in turn, was refluxed for an additional two andone-half hours to produce a golden yellow solid.

The slurry was cooled to room temperature, the liquid decanted and thesolid washed five times, each time with hexane (150 ml). The solvent wasevaporated, utilizing a nitrogen purge followed by vacuum, to yield 31.1grams of a pale yellow solid.

EXAMPLE 2

Copolymerization of Ethylene and 1-Butene

A one-gallon reactor was filled with 190 ml of 1-butene and 1200 ml ofisobutane. The reactor was heated to 170° F. To the thus heated contentsof the reactor were added 0.02 gram of the catalyst formed in Example 1and 1 ml of a 25 weight percent solution of triethylaluminum in hexane.The reactor was sealed and pressurized with hydrogen (29 psi) andethylene (123 psi). In addition, ethylene gas was fed into the reactoron demand during the polymerization reaction. After conducting thepolymerization reaction for one hour, the contents of the reactor wereremoved and the volatile liquids evaporated.

The polymer product obtained in this reaction, 227 grams, wascharacterized by a melt index, as measured by ASTM D-1238, of 1.35, amelt index ratio (MIR) of 42.3 and a density of 0.9205.

COMPARATIVE EXAMPLE 1 (CE 1)

Preparation of Prior Art Catalyst

Silicon tetrachloride (0.14 mole, 16 ml), dissolved in heptane (75 ml),was added to a 500 ml, four-necked flask provided with a 60 ml additionfunnel, condenser, thermometer and mechanical stirrer. The silicontetrachloride solution was then heated to reflux temperature whereupon a0.68M solution of dibutylmagnesium in heptane (0.07 mole, 103 ml) wasadded and the contents refluxed for one hour. The product of thisreaction was a white solid. To the thus formed slurry was added,dropwise, ethanol (0.14 mole, 8.2 ml), dissolved in heptane (15 ml). Theslurry was refluxed for one hour whereupon titanium tetrachloride (0.07mole, 7.7 ml), dissolved in heptane (15 ml), was added. An additionaltwo hours of refluxing followed this addition.

The slurry was then cooled to room temperature, the liquid decanted andthe solid washed five times with hexane (100 ml). The remaining solventwas evaporated, with a nitrogen purge followed by vacuum, to yield 9.6grams of a cream-colored solid.

COMPARATIVE EXAMPLE 2 (CE 2) Copolymerizing Ethylene and 1-Butene WithPrior Art Catalyst

A copolymer of ethylene and 1-butene was formed in accordance with theprocedure of Example 2 except that 0.001 g of the catalyst formed inaccordance with Comparative Example 1 was substituted for the catalystof Example 1. The sealed reactor was pressurized with hydrogen (42 psi)and ethylene (120 psi).

It is noted that the reason for this diminished concentration ofcatalyst, only 5% by weight as much as that used in Example 2, isbecause the prior art catalyst, although inferior to the catalyst ofExample 1 for the reasons given hereinafter, is far more active. Inorder to obtain a similar polymeric yield, therefore, the catalystconcentration of this example was significantly reduced.

The polymer obtained in this reaction, 181 grams, was characterized by amelt index, as measured by ASTM D-1238, of 1.04, a melt index ratio(MIR) of 42.3 and a density of 0.9269.

DISCUSSION OF EXAMPLES 1, 2, CE1 and CE2

The catalyst formed in Example 1, in accordance with the presentinvention, produced an especially effective LLDPE, as evidenced byExample 2. On the other hand, the catalyst representative of the closestprior art, the catalyst of Comparative Example 1, produced a lesseffective LLDPE, as evidenced by Comparative Example 2.

The LLDPE of Example 2 was characterized by a melt index of 1.35. Toproduce this acceptable degree of polymerization, only 29 psi ofhydrogen gas was maintained in the reactor during the polymerizationreaction. To produce a slightly less effective, but still satisfactoryLLDPE, characterized by a higher melt index of 1.04, utilizing the priorart catalyst of Comparative Example 1, required a higher hydrogenconcentration than that required in Example 2. Thus, in ComparativeExample 2 a hydrogen pressure of 42 psi, compared to only 29 psi inExample 1, was required. This result emphasizes the improved hydrogenresponse of the catalyst of the present invention over that of theclosest prior art.

Similarly, the polymerization reaction of Example 2 was conducted with acharge of 190 ml of 1-butene. This polymerization reaction, using thecatalyst of the present invention, formulated in Example 1, produced 227grams of polymer having a density of 0.9205. However, the same quantityof 1-butene, utilizing substantially the same concentration of ethylene,120 psi vs. 123 psi, in Example 2, produced only 181 grams of polymer ofa higher density, 0.9269 g/cc. This result evidences the greateralpha-olefin incorporation capability of the catalyst of the presentinvention over that of the closest prior art. Moreover, the aim ofproducing a linear low density polyethylene is obviously moresuccessfully met utilizing the catalyst of the present invention in thatthe polyethylene has a significantly lower density.

EXAMPLE 3 Preparation of Catalyst

The preparation of a reaction product of silicon tetrachloride,dibutylmagnesium and ethanol was conducted in exact accordance with theprocedure of Example 1. Thereafter, this reaction product, slurried inheptane, was refluxed for one hour, rather than the one-half hour ofExample 1. To this slurry was added titanium tetrachloride (0.035 mole,3.85 ml), dissolved in heptane (10 ml). This mixture was refluxed fortwo hours. Aluminum tri-sec-butoxide (0.07 mole, 17.8 ml), dissolved inheptane (20 ml), was added and refluxed together with the white solidreaction product for an additional one-half hour. Titanium tetrachloride(0.15 mole, 15.4 ml) was added to this product followed by refluxing foran additional two hours.

The reaction mixture was cooled to room temperature, the liquid decantedand the solid washed five times, each time with hexane (100 ml). Theremaining solvent was evaporated, with a nitrogen purge followed byvacuum, to yield 17.1 grams of a pale yellow solid.

EXAMPLE 4 Copolymerization of Ethylene and 1-Butene

Ethylene and 1-butene were copolymerized in accordance with theprocedure of Example 2, except that 266 ml of 1-butene, rather than the190 ml used in Example 2, and 0.011 gram of the catalyst prepared inExample 3, rather than the 0.02 gram of the catalyst of Example 1, wereused. The reactor was pressurized with 47 psi hydrogen and 119 psiethylene.

The result of this polymerization reaction was the obtaining of 170grams of polymer characterized by a melt index of 1.97, an MIR of 43.9and a density of 0.9201.

EXAMPLE 5 Preparation of Catalyst

Silicon tetrachloride (0.14 mole, 16 ml), aluminum tri-sec-butoxide(0.0175 mole, 4.5 ml) and heptane (75 ml) were added to a 500 ml flaskof the type defined in Example 1. The solution was then heated to refluxtemperature. A 0.68M solution of dibutylmagnesium in heptane (0.07 mole,103 ml) was added thereto and the contents refluxed for one hour toproduce a white solid. Ethanol (0.14 mole, 8.2 ml), dissolved inheptane. (15 ml), was added dropwise thereto. After refluxing for onehour, titanium tetrachloride (0.07 mole, 7.7 ml), dissolved in heptane(10 ml), was added and refluxing continued for an additional one andone-half hours. Aluminum tri-sec-butoxide (0.035 mole, 8.9 ml),dissolved in heptane (10 ml), was added and refluxed with the whitesolid slurry for one-half hour. Titanium tetrachloride (0.14 mole, 15.4ml) was then added, followed by refluxing for an additional three hours.

The reaction mixture was cooled to room temperature and allowed to standovernight. The liquid was then decanted and the solid washed five times,each time with hexane (150 ml). The remaining solvent was evaporatedwith a nitrogen purge followed by vacuum to give 19.1 grams of a paleyellow solid.

EXAMPLE 6 Copolymerization of Ethylene and 1-Butene

Ethylene and 1-butene were copolymerized in accordance with the generalprocedure of Example 2. However, the amounts of the reactants were notidentical with those of Example 2. The amount of 1-butene charged was266 ml. Moreover, the catalyst utilized in the polymerization of Example2, the catalyst of Example 1, was replaced with the catalyst formed inExample 5 in an amount of 0.009 gram. The polymerization reactor, inthis example, was pressurized with hydrogen (34 psi) and ethylene (122psi).

The polymer product of this reaction was obtained in a quantity of 282grams. It was characterized by a melt index of 1.34, an MIR of 34.0 anda density of 0.9219.

EXAMPLE 7 Preparation of Catalyst

A reaction product of silicon tetrachloride, dibutylmagnesium andethanol was produced in accordance with the procedure of Example 1except that this reaction product was refluxed for one hour, rather thanthe one-half hour used in Example 1. The procedure of Example 1 was alsofollowed in the reaction of this reaction product with titaniumtetrachloride but for the refluxing of this reaction for one andone-half hours, rather than the two hours of Example 1.

To this reaction product was added aluminum tri-sec-butoxide (0.035mole, 8.9 ml), dissolved in heptane (10 ml), followed by the addition oftitanium tetrachloride (100 ml). Upon addition of these two componentsto the reaction product in the flask, the contents of the flask wereheated to reflux temperature for two hours, reaching an ultimatetemperature of 117° C.

The contents were then cooled to room temperature, the liquid decantedand the solvent washed seven times with hexane (150 ml). The remainingsolvent was evaporated with a nitrogen purge followed by vacuum toprovide 18.7 grams of a brownish-gold solid.

EXAMPLE 8 Copolymerization of Ethylene and 1-Butene

Ethylene and 1-butene were copolymerized in accordance with theprocedure in Example 2 except that the catalyst of Example 7 wassubstituted for the catalyst of Example 1 and was present in an amountof 0.003 gram. The concentration of 1-butene was 342 ml and the reactorwas pressurized with 32 psi of hydrogen and 123 of psi of ethylene.

The polymer obtained amounted to 232 grams and was characterized by amelt index of 2.43, an MIR of 41.1 and a density of 0.9102.

EXAMPLE 9

Preparation of Catalyst

A reaction product of silicon tetrachloride, dibutylmagnesium, ethanoland titanium tetrachloride was formed in exact accordance with theprocedure of Example 7. At this point, the reaction product, in aheptane slurry, was cooled to room temperature, the liquid decanted andthe solid washed once with heptane (50 ml).

Aluminum tri-sec-butoxide (0.035 mole, 8.9 ml) and heptane (100 ml) wereadded and refluxed with the white solid reaction product for one-halfhour. Vanadium oxytrichloride (0.07 mole, 6.6 ml), dissolved in heptane(10 ml), was added, followed by refluxing for one and one-half hours.

After cooling to room temperature, the liquid was decanted and the solidwashed five times with hexane (150 ml). The remaining solvent wasevaporated with a nitrogen purge followed by vacuum to give 17.4 gramsof a gray solid.

EXAMPLE 10 Copolymerization of Ethylene and 1-Butene

Ethylene and 1-butene were copolymerized in accordance with theprocedure of Example 2 except that 266 ml of 1-butene and 0.31 gram ofthe catalyst, prepared in accordance with Example 9, were used. Thereactor was pressurized with 28 psi of hydrogen and 123 psi of ethylene.

The polymer obtained had a melt index of 1.35, an MIR of 59.9 and adensity of 0.9184. It was obtained in a yield of 329 grams.

EXAMPLE 11 Preparation of Catalyst

A reaction product of silicon tetrachloride, dibutyl magnesium, ethanoland titanium tetrachloride were formed in accordance with the procedureof Example 7 except that the reaction product of the first three namedcomponents with titanium tetrachloride was refluxed for two hours,rather than one and one-half hours. The slurry of the reaction productof the four components was then cooled to room temperature, the liquiddecanted and the solid washed five times with hexane (100 ml).

Another 125 ml of hexane was added to the washed reaction product andthe slurry heated to reflux temperature. Aluminum tri-sec-butoxide (0.07mole, 17.8 ml) was added to the washed reaction product and refluxedtogether with the white solid reaction product for one hour. Titaniumtetrachloride (0.14 mole, 15.4 ml), dissolved in hexane (15 ml), wasadded, followed by refluxing for two hours.

After cooling to room temperature, the liquid was decanted and the solidwashed five times with hexane (100 ml). The remaining solvent wasevaporated with a nitrogen purge followed by vacuum to give 22.5 gramsof a straw colored solid.

EXAMPLE 12 Copolymerization of Ethylene and 1-Butene

Ethylene and 1-butene were copolymerized in accordance with theprocedure of Example 2 except that 0.01 gram of the catalyst prepared inExample 11 replaced the catalyst of Example 1 and that the amount of1-butene charged was 266 ml. The reactor was pressurized with hydrogenand ethylene, as in Example 2. However, the hydrogen was charged at apressure of 20 psi and the ethylene at a pressure of 125 psi.

The polymer obtained amounted to 205 grams and had a melt index of 1.84,an MIR of 42.7 and a density of 0.9109.

COMPARATIVE EXAMPLE 3 Copolymerization of Ethylene and 1-Butene

Ethylene and 1-butene were copolymerized in accordance with theprocedure of Example 2 except that 266 ml of 1-butene and 0.001 gram ofthe catalyst prepared in Comparative Example 1 were used. The reactorwas pressurized with 43 psi of hydrogen and 120 psi of ethylene.

The polymer thus produced was obtained in the yield of 113 grams and wascharacterized by a melt index of 1.15, an MIR of 32.5 and a density of0.9220.

EXAMPLE 13 Preparation of Catalyst

A reaction product of silicon tetrachloride, dibutylmagnesium, ethanoland titanium tetrachloride was formed in accordance with the procedureof Example 11. Thereafter, the reaction product was slurried in 100 mlof hexane and half of the slurry removed to another container.

The slurry remaining in the 500 ml flask was diluted with another 75 mlof hexane. Aluminum tri-sec-butoxide (0.0175 mole, 4.45 ml) was addedand refluxed with the white solid reaction product for one hour.Titanium tetrachloride (0.07 mole, 7.7 ml), dissolved in hexane (10 ml),was added, followed by refluxing for two hours to produce a yellowsolid.

After cooling to room temperature, the liquid was decanted and the solidwashed five times with hexane (100 ml). The remaining solvent wasevaporated with a rotary evaporator to yield 8.4 grams of solid.

EXAMPLE 14 Copolymerization of Ethylene and 1-Butene

Ethylene and 1-butene were copolymerized in accordance with theprocedure of Example 1 except that 0.003 gram of the catalyst formed inExample 13 was used. The reaction was pressurized with 22 psi ofhydrogen and 125 psi of ethylene.

The yield of the polymer obtained in this polymerization reaction was230 grams and was characterized by a melt index of 1.24, an MIR of 38.5and a density of 0.9201.

EXAMPLE 15 Preparation of Catalyst

Silica (10 g.), previously dried at 1100° F., hexane (75 ml.) anddibutylmagnesium (51 ml. of a 0.68M solution in hexane) were introducedinto a 500 ml. three-necked flask equipped with a condensor, a 60 ml.addition funnel and a mechanical stirrer. The flask was heated toboiling without cooling. The hexane evaporated leaving a mud-likeproduct. The product was cooled to ambient temperature. Thereupon,heptane (75 ml.) was added to the mud and resultant slurry was heated toreflux temperature. Silicon tetrachloride (8 ml., 0.07 mole) dissolvedin heptane (25 ml.) was added to the slurry which was then heated atreflux for 30 minutes. Ethanol (4.1 ml., 0.07 mole) dissolved in heptane(10 ml.) was then introduced into the slurry and heating at reflux wascontinued for an additional 30 minutes. A solution of titaniumtetrachloride (7.7 ml., 0.07 mole) in heptane (10 ml.) was added andheating at reflux was maintained for another 45 minutes. After coolingto room temperature, the liquid was decanted and the solid product waswashed 5 times with hexane (100 ml.). The washed solid was reslurried inheptane (125 ml.) and aluminum tri-sec-butoxide (4.45 ml., 0.0175 mole)was added thereto. The slurry was heated for two hours at refluxtemperature. To this slurry was added a second charge of titaniumtetrachloride (3.85 ml., 0.035 mole) dissolved in heptane (10 ml.). Theslurry was again heated at reflux for yet another two hours.

After cooling to ambient temperature the liquid was decanted and thesolids remaining were washed six times with hexane (100 ml.). Theremaining solvent was evaporated utilizing a nitrogen purge followed byvacuum. The result was a pale yellow solid (24.0 g.).

EXAMPLE 16 Copolymerization of Ethylene and 1-Butene

A 1 gallon reactor was filled with 1-butene (266 cc.) and isobutane(1200 ml.) and heated to 76.5° C. To the contents of the reactor wasadded catalyst (0.035 g.) formed in accordance with the procedure ofExample 15 along with a 25 wt % solution of triethylaluminum in hexane(1.0 cc.). The reactor was sealed and pressurized with hydrogen (34 psi)and ethylene (122 psi). The reactor was maintained at these conditionsfor 1 hour. During this time ethylene was fed into the reactor ondemand. After 1 hour the reactor contents were removed and the volatileliquids evaporated.

The product of this reaction was a polymer (409 g.) characterized by amelt index of 1.63 and a density of 0.9171 g/cc.

The above embodiments and examples are given to illustrate the scope andspirit of the present invention. These embodiments and examples willmake apparent, to those skilled in the art, other embodiments andexamples. These other embodiments and examples are within thecontemplation of the present invention. Therefore, it is understood thatthe instant invention is limited only by the appended claims.

What is claimed is:
 1. A process for the polymerization of at least onealpha-olefin comprising polymerizing at least one alpha-olefin, underpolymerization conditions, in the presence of(1) a catalyticallyeffective amount of a catalyst comprising the reaction product of:(a) asilicon-containing compound having the structural formula R_(4-n)SiX_(n), where R is C₁ -C₁₀ hydrocarbyl; X is halogen; and n is aninteger of 1 to 4; (b) a magnesiumdialkyl having the structural formulaR¹ R² Mg, where R¹ and R² are the same or different and are C₂ -C₁₀alkyl; (c) an alcohol having the structural formula R³ OH, where R³ isC₁ -C₁₀ hydrocarbyl; (d) a halide-containing metal compound, said metalselected from the group consisting of titanium, zirconium and vanadium;(e) an aluminum alkoxide having the structural formula Al(OR⁵)₃, whereR⁵ is C₂ -C₄ alkyl; and (f) a halide-containing metal compound, saidmetal selected from the group consisting of titanium, zirconium andvanadium, with the proviso that said reaction product is formed fromsaid components reacted in the order recited but for theinterchangeability of components (a) and (b); and (2) a co-catalyticallyeffective amount of an organoaluminum compound.
 2. A process for thepolymerization of alpha-olefins comprising polymerizing at least onealpha-olefin, under polymerization conditions, in the presence of(1) acatalytically effective amount or a catalyst comprising the reactionproduct of:(a) a silicon-containing compound having the structuralformula R_(4-n) SiX_(n), where R is C₁ -C₁₀ hydrocarbyl; X is halogen;and n is an integer of 1 to 4; (b) a magnesiumdialkyl having thestructural formula R¹ R² Mg, where R¹ and R² are the same or differentand are C₂ -C₁₀ alkyl; (c) an alcohol having the structural formula R³OH, where R³ is C₁ -C₁₀ hydrocarbyl; (d) a halide-containing metalcompound, said metal selected from the group consisting of titanium,zirconium and vanadium; (e) an aluminum alkoxide having the structuralformula Al(OR⁵)₃, where R⁵ is C₂ -C₄ alkyl; and (f) a halide-containingmetal compound, said metal selected from the group consisting oftitanium, zirconium and vanadium, with the proviso that said reactionproduct is formed from said components reacted in the order recited butfor the interchangeability of components (a) and (b), wherein saidcomponent (a) is reacted with an aluminum alkoxide having the structuralformula Al(OR⁵)₃, where R⁵ is C₂ -C₄ alkyl, which product is reactedwith said component (b), and (2) a co-catalytically effective amount ofa trialkyl aluminum compound having the structural formula AlR⁶ ₃, whereR⁶ is C₁ -C₆ alkyl.
 3. A process for the polymerization of at least onealpha-olefin comprising polymerizing at least one alpha-olefin underpolymerization conditions in the presence of(1) a catalyticallyeffective amount of a catalyst comprising a reaction product of:(a) asilicon-containing compound having the structural formula R_(4-n)SiX_(n), where R is C₁ -C₁₀ hydrocarbyl; X is halogen; and n is aninteger of 1 to 4; (b) dibutylmagnesium; (c) ethanol; (d) titaniumtetrachloride; (e) aluminum tri-sec-butoxide; and (f) a compoundselected from the group consisting of titanium tetrachloride andvanadium oxytrichloride with the proviso that said reaction productresults from the reaction of said components (a) to (f) reacted in theorder recited, and (2) a co-catalytically effective amount of atrialkylaluminum compound.
 4. A process for the polymerization of atleast one alpha-olefin comprising polymerizing at least one alpha-olefinunder polymerization conditions in the presence of(1) a catalyticallyeffective amount of a catalyst comprising a reaction product of:(a) asilicon-containing compound having the structural formula R_(4-n)SiX_(n), where R is C₁ -C₁₀ hydrocarbyl; X is halogen; and n is aninteger of 1 to 4; (b) dibutylmagnesium; (c) ethanol; (d) titaniumtetrachloride; (e) aluminum tri-sec-butoxide; and (f) a compoundselected from the group consisting of titanium tetrachloride andvanadium oxytrichloride with the proviso that (I) said reaction productresults from the reaction of said components (a) to (f) reacted in theorder recited and (II) said reaction product includes silica introducedin said reaction product before or simultaneously with said component(a), and (2) a co-catalytically effective amount of triethylaluminum. 5.A process in accordance with claim 1 wherein said organoaluminumcompound is a trialkylaluminum compound having the structural formulaAlR⁶ ₃, where R⁶ is C₁ -C₁₀ alkyl.
 6. A process in accordance with claim5 wherein R⁶ is C₁ -C₆ alkyl.
 7. A process in accordance with claim 6wherein said alpha-olefin is ethylene.
 8. A process in accordance withclaim 6 wherein said alpha-olefin is ethylene and an alpha-olefinselected from the group consisting of C₃ -C₁₀ alpha-olefins.
 9. Aprocess in accordance with claim 8 wherein said alpha-olefin is ethyleneand 1-butene.
 10. A process in accordance with claim 9 wherein R⁶ isethyl.